Every RV solar setup needs a charge controller between the panels and the battery - it regulates the panel output so it charges your battery safely. There are two types: PWM and MPPT. Here's the difference and which one belongs in your camper.
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What a charge controller does
Solar panels produce more voltage than your battery wants, and that voltage swings with sunlight. The controller regulates it to a safe, multi-stage charge so you don't overcharge or undercharge the bank. The two technologies do this very differently.
PWM, in short
A PWM (Pulse Width Modulation) controller essentially connects the panel directly to the battery and rapidly switches to hold the right voltage. It's simple and inexpensive, but it pulls the panel down to battery voltage - so the extra voltage your panel could produce is wasted. PWM works best when panel voltage is close to battery voltage and arrays are small.
MPPT, in short
An MPPT (Maximum Power Point Tracking) controller is a smart DC-DC converter. It runs the panel at its most efficient voltage, then converts the excess voltage into extra charging current - so you capture energy a PWM would throw away. In real conditions MPPT typically harvests roughly 20-30% more energy, and the gain is biggest in cold or low-light conditions and with higher-voltage arrays.
MPPT vs PWM: the quick comparison
| Factor | PWM | MPPT |
|---|---|---|
| Efficiency | Lower (panel pulled to battery voltage) | Higher (harvests excess voltage as current) |
| Energy harvest | Baseline | ~20-30% more, typically |
| Higher-voltage arrays / panels in series | Not suitable | Designed for it |
| Cost | Lower | Higher |
| Best for | Small, low-voltage setups | Most RV solar, especially 200W+ or cold climates |
Which should you choose?
For nearly all RV solar setups - especially anything around 200W or more, panels wired in series, or camping in cold/variable light - an MPPT controller is the better investment; the extra harvest pays back quickly. PWM only makes sense for very small, budget systems with a single low-voltage panel. Victron's SmartSolar MPPT range adds Bluetooth monitoring so you can watch yield from your phone.
Sizing an MPPT controller
MPPT controllers are rated like 100/30 - the first number is the maximum panel voltage, the second is the charge current (amps) to the battery. Choose one whose voltage rating exceeds your array's open-circuit voltage and whose current rating matches your panel wattage divided by battery voltage. When in doubt, size up for headroom.
Frequently asked questions
Is MPPT always worth it?
For most RVs, yes - the extra 20-30% harvest and support for higher-voltage arrays usually outweigh the higher price. Very small single-panel setups can still use PWM.
Can I wire panels in series with MPPT?
Yes - MPPT controllers are built for higher array voltages, and series wiring helps them work efficiently. PWM cannot take advantage of this.
How does this fit my whole system?
The controller feeds your battery bank; see how to build a full Victron off-grid system for the complete picture.
Browse solar charge controllers and RV solar panels & kits. Ships from Upland, CA.